HPAEC-PAD, biochemical characterization, and evaluation of the antioxidants activities of polysaccharides extracted from Olive Mill Wastewater of two endemic varieties of Khenchela region, Algeria

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Olive Mill Wastewater (OMWW) is considered to be one of the by-products of the extraction of olive oil that causes serious problems to the environment. This study describes a qualitative and quantitative analysis of biochemical characterizations and assessment of polysaccharides antioxidant activities from cold extraction of two endemic varieties from Khenchela region, eastern Algeria. As a result, the physicochemical characteristics of these OMWWs (Chemlal and Ferkani) were found to be acidic (pH: 4.77–5.1) and saline (1.35–1.40 mg/l). According to Chemlal and Ferkani, the dry matter (DM), total suspended solids (TSS) and mineral matter (MM) are respectively (159.3 ± 14.03 g/L, 4.13 ± 0.04 g/L, 10 ± 0.5 g/L and (117.4 ± 12.03 g/L, 1.06 ± 0.1 g/L, 9.7 ± 1 g/L). In addition, the COD and DBO5 requirements are (9625.6 ± 13.42 mg/l; 45 ± 08 mg/l for Chemlal) and (10490.6 ± 23.84 mg/l; 440 ± 3 mg/l for Ferkani) respectively. Due to their high content of organic matter and mineral salts, the OMWW studied have very little potential for biodegradation. Three extracts were prepared for each cultivar: insoluble alcohol fraction (AIR), soluble water fraction (SF) and insoluble water fraction (IF). The biochemical characterisation was carried out by colorimetric assays using an appropriate spectrophotometer for the determination of total sugars (OT), reducing sugars (OR), neutral sugars, protein, nitrogen and phenolic compounds. The qualitative and quantitative analysis of the polysaccharides was carried out using high- performance anion-exchange chromatography coupled with pulsed amperometric detection (HPAEC-PAD). The results obtained showed heterogeneous composition of nine monosaccharides for each fraction at different levels. The total dry matter (%DM) of the Chemlal fractions (AIRC, SFC, IFC) are respectively (14.44%, 16.93%, 15.68%) and those of the Ferkani fractions (AIRF, SFF, IFF) are respectively (10%, 15.05%, 10.52%). The antioxidant activities of two soluble fractions (SFC and SFF) were evaluated using five assays: DPPH, ABTS, CUPRAC, phenthroline and hydrogen peroxide, when the best antioxidant activity is provided by hydrogen peroxide.